In order to attain a particular lift during slow flight, modern commercial aircraft may require high lift devices during the takeoff and landing phases. During the takeoff phase, high lift devices are used to generate a high coefficient of lift combined with little resistance and a low noise level. Likewise, these conditions apply during the landing phase, wherein in this case, the low resistance plays a subordinate role because resistance makes it possible to concurrently reduce the aircraft speed.
Up to now, high lift devices or additional flaps have been affixed to airfoils or wings and have been extended or retracted or swivelled as required. In this arrangement, so-called slats can be activated on the leading edge of the wing, and so-called flaps can be activated on the trailing edge of the wing in order to have an influence on the wing surface and/or the wing geometry.
The geometry and the surface of the wing profile may have a decisive influence on the flight characteristics of an aircraft, in particular at critical flight states, e.g. during the takeoff or landing phases. Since, as a rule, an aircraft spends by far the greatest part of its time cruising, the wing profiles may be optimised most of the time to this flight state so that additional measures have to be taken for takeoff and landing. In this context, increasing the maximum lift may play an important role in order to shorten the takeoff distance or in order to achieve minimum landing speed during landing. In order to meet these two opposing requirement profiles, namely high lift during takeoff and landing versus the best possible economy during cruising, the geometry of wing profiles may be varied with the use of flap systems.
The profile surface is controlled by intended extension and retraction of high lift devices such that the size of the wing surface changes. On the other hand, it is possible to swivel high lift devices, as a result of which the profile curvature can be adjusted. With an increase in the profile curvature and with a larger wing surface the airflow on the underside of the wing is increasingly decelerated and on the top of the wing is accelerated such that the pressure gradient between the top and the underside of the wing increases and a higher coefficient of lift results.
Several flap systems have been designed that have different effects on flight characteristics. The normal wing flap is arranged between the aileron and the fuselage, on the rear airfoil end. As a rule, the wing flap can deflect downward only; it is primarily used to change the profile curvature, as a result of which higher lift and higher resistance are generated.
One embodiment of the wing flap is the slotted flap. The slotted flap, too, may only deflect downwards. When compared to the wing flap, the slotted flap has a slot between the wing and the high lift device, through which slot air can flow from the underside of the wing to the top.
The Fowler flap is a further embodiment of the wing flap. In principle, the Fowler flap is a slotted flap which not only hinges downward but may also be extended towards the rear. Apart from an increase in the curvature, this may additionally provide a larger wing surface.
Already in the takeoff position, the high lift devices are extended in order to increase lift and thus reduce the take-off speed that is required. As a result of this, the slot already opens, although stall on the flap is not expected as yet.
U.S. Pat. No. 6,601,801 B1 discloses a device in which a slot that results in the aileron of an aircraft may be regulated by an additional element. This additional element is mechanically force-controlled or guided and moves on a fixed axis when the aileron is deflected.
This may result in the lift generated by the high lift devices being reduced correspondingly (pressure equalisation between the top and the underside) and in the noise level being increased (high air-flow speed in the slot).